E. coli bacteria trigger mucin reduction to promote a destabilized epithelial barrier in SBP

Background:

Spontaneous bacterial peritonitis is a life-threatening complications of liver cirrhosis, that is driven by bacterial translocation. Bacterial translocation means that commensal gut bacteria translocate paracellular via dysregulated cell-to-cell contact proteins to mesenteric lymph nodes. Although a disrupted intestinal epithelial barrier of patients with liver cirrhosis and SBP have already been shown by us, we and others do not know the detailed mechanisms of SBP development. Therefore, we established a clinically relevant Caco-2 model to identify molecular mechanisms of bacterial translocation.

Methods:

Caco-2 cells were cultivated for six days and treated with different concentrations of E. coli bacteria that were isolated from ascitic fluid of two patients with liver cirrhosis and SBP. As control, heat-inactivated bacteria (65 °C, 5 min) and E. coli LPS O55:H5 (0,1 and 1 µg/ml) were used for stimulation of Caco-2 cells. For the study of mechanisms of paracellular bacterial translocation, cell-to-cell contact proteins (E-cadherin and occludin) were examined on RNA and protein level. Caco-2 cells were stimulated with E. coli bacteria directly or via a semipermeable membrane. In addition, mucin regulation (MUC-2 and MUC5AC) of Caco-2 cells were analyzed on RNA level after cells were incubated with SBP E. coli bacteria.

Results:

Bacterial stimulation with E. coli, isolated of patients with liver cirrhosis and SBP, resulted in a decrease of E-cadherin and occludin of Caco-2 cells. The reduction intensity was dependent on the E. coli strain that was used for stimulation. Heat-inactivated bacteria and LPS failed to induce any changes. If Caco-2 cells were incubated with E. coli bacteria directly, a greater downregulation, especially for E-cadherin was shown. Moreover, SBP E. coli bacteria reduced mucin production of Caco-2 cells.

Conclusion:

For a paracellular translocation, E. coli bacteria destabilize intestinal epithelial barrier via dysregulated cell-to-cell contact proteins. Direct interaction of E. coli bacteria and intestinal epithelial cells promote downregulation of cell-to-cell contact proteins. Therefore, SBP E. coli bacteria trigger downregulation of mucin regulation to facilitate a physical interaction of bacteria and the intestinal epithelium.